When a subject's eye is affected by dry eye, there is a risk that it will complicate corneal epithelial disorders, conjunctival disorders, and various other ophthalmic diseases. Therefore, the anterior ocular segment of a subject's eye is observed or photographed to diagnose the dry eye and other symptoms. For example, the degree of advancement of dry eye is qualitatively diagnosed through observation of interference stripes formed by the tear fluid in the anterior ocular segment of the subject's eye (Patent Document 1). In this case, it is known that the anterior ocular segment can be satisfactorily observed or photographed when a beam of light incident on the cornea via a projection system is made to enter the surface of the cornea in a vertical direction in order to efficiently condense reflection from the cornea (Patent Document 2).
Furthermore, a lattice-shaped slit is projected on the anterior ocular segment of a subject's eye, and the physical quantity of tear fluid accumulated on the anterior ocular segment is quantitatively measured to diagnose dry eye based on the aperture image of the slit (Patent Document 3).
Patent Document 1: JP-A 1995-136120
Patent Document 2: JP-A 1997-289970
Patent Document 3: JP-A 1999-267102